1 use core::pin::Pin; 2 use futures_core::ready; 3 use futures_core::stream::{FusedStream, Stream}; 4 use futures_core::task::{Context, Poll}; 5 #[cfg(feature = "sink")] 6 use futures_sink::Sink; 7 use pin_project_lite::pin_project; 8 9 pin_project! { 10 /// Stream for the [`skip`](super::StreamExt::skip) method. 11 #[derive(Debug)] 12 #[must_use = "streams do nothing unless polled"] 13 pub struct Skip<St> { 14 #[pin] 15 stream: St, 16 remaining: usize, 17 } 18 } 19 20 impl<St: Stream> Skip<St> { new(stream: St, n: usize) -> Self21 pub(super) fn new(stream: St, n: usize) -> Self { 22 Self { stream, remaining: n } 23 } 24 25 delegate_access_inner!(stream, St, ()); 26 } 27 28 impl<St: FusedStream> FusedStream for Skip<St> { is_terminated(&self) -> bool29 fn is_terminated(&self) -> bool { 30 self.stream.is_terminated() 31 } 32 } 33 34 impl<St: Stream> Stream for Skip<St> { 35 type Item = St::Item; 36 poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>>37 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St::Item>> { 38 let mut this = self.project(); 39 40 while *this.remaining > 0 { 41 if ready!(this.stream.as_mut().poll_next(cx)).is_some() { 42 *this.remaining -= 1; 43 } else { 44 return Poll::Ready(None); 45 } 46 } 47 48 this.stream.poll_next(cx) 49 } 50 size_hint(&self) -> (usize, Option<usize>)51 fn size_hint(&self) -> (usize, Option<usize>) { 52 let (lower, upper) = self.stream.size_hint(); 53 54 let lower = lower.saturating_sub(self.remaining); 55 let upper = upper.map(|x| x.saturating_sub(self.remaining)); 56 57 (lower, upper) 58 } 59 } 60 61 // Forwarding impl of Sink from the underlying stream 62 #[cfg(feature = "sink")] 63 impl<S, Item> Sink<Item> for Skip<S> 64 where 65 S: Stream + Sink<Item>, 66 { 67 type Error = S::Error; 68 69 delegate_sink!(stream, Item); 70 } 71